The present invention relates to a gas discharge panel for data display and a method for driving same. In particular, a novel panel structure and driving method attain long life of an AC surface discharge or monolithic type gas discharge panel and stable operation with a wide operating margin.
In gas discharge panels, known as plasma display panels, surface discharge or monolithic type display panels utilize lateral discharges between adjacent electrodes. Basically, as is disclosed in U.S. Pat. No. 3,646,384, issued to F. M. Lay, in a monolithic gas discharge panel of this type the electrodes are disposed only on one substrate of a pair of substrates and are separated by a dielectric layer or layers. The electrodes on opposite sides of the dielectric layer are arranged to intersect and the intersections define discharge cells. The pair of substrates oppose each other and define a gap or space which is filled with a discharge gas. This structure provides the advantages of alleviating the requirement of an accurate gap spacing and the realization of multi-color displays which are created by coating the internal surface of the non-electrode bearing substrate with an ultraviolet ray excitation type phosphor. With the structure of the conventional panel, however, satisfactory panel life and operating margin could not be attained because the dielectric layer become damaged due to a concentration of the discharge current at portions of the dielectric layer corresponding to edges of the electrodes. Therefore, Japanese Unexamined Patent Publication No. 57-78751, having a common inventor with the present patent, proposes a panel structure which is improved by separating the functions of write cells and display cells in order to elongate the life of the panel. The conventional panel structure can be understood from a plan view of electrode layout, as shown in FIG. 1, and a partial sectional view as shown in FIG. 2.
With respect to FIGS. 1 and 2, longitudinal sustaining electrode pairs 2, 3 are provided on the rear side or electrode-bearing glass substrate 1 which functions as an electrode supporting substrate. The sustaining electrodes 2, 3 have protrusions 2a, 3a of a comb or tooth-like structure, the protrusions on adjacent electrodes forming pairs, and discharge cells Dc are defined by each pair of the comb or tooth-like protrusions 2a, 3a. Write or address electrodes 5 are disposed laterally on a vacuum-deposited layer 4 which is formed of boron silicate glass and which separates the write or address electrodes 5 from the sustaining electrode pairs 2, 3. A layer 6 of boron silicate glass is vacuum-deposited over the wirte or address electrodes 5 and a surface protection layer 7 of MgO is formed over the boron silicate glass layer 6. Write or address cells Wc are defined at the intersecting points of the write electrodes 5 and any one of the sustaining electrodes 2, 3. An upper or front glass substrate 8 opposes the electrode bearing substrate 1. A seal is formed between the edges of the electrode-bearing substrate 1 and the upper glass substrate 8, the gap 9 between the substrates is evacuated, and a discharge gas is introduced into the gap 9 between them, thus completing a panel.
Discharges are generated at the write cells Wc when a voltage higher than a discharge start voltage is applied to the write cells Wc. Thereafter, a sustaining voltage which is lower than the discharge start voltage is repeatedly applied alternately to the corresponding sustaining electrodes 2 and 3 so that the write discharge is transferred to the adjacent display cell Dc in order to continuously sustain the discharges. By separating a picture element into two kinds of cells, i.e., write cells and display cells, the amount of time during which the concentration of current is located at the display cell Dc is decreased. Further, the large voltage necessary to generate a discharge is not applied to the display cell.
As described above, the panel structure disclosed in the Japanese Unexamined Patent Publication No. 57-78751, can extend service life by alleviating damage to the dielectric layer. However, a comparatively thick dielectric layer 6 (about 6 .mu.m) and a surface protection layer 7 (about 0.5 .mu.m) are formed on the address or write electrodes 5 in this panel, and therefore wall charges, generated by the discharges, accumulate on the portions of the surface protection layer corresponding to the positions of the write electrodes. The accumulation of such abnormal wall charges produces defective displays or improper discharges.
When discharges are generated at the write cells, charges are accumulated on the surface of surface protection layer 7 correspnding to the relevant write cells Wc and the areas near such cells. The amount of charge which accumulates on the surface protection layer 7 at positions corresponding to the write cells Wc gradually increases as discharges occur at the display cells Dc until an abnormal field, resulting from the accumulation of excess wall charges, in cooperation with an external field, such as a sustaining voltage, induces an accidental discharge at the area near the relevant write cells.